Generally, for an HDTV, a television broadcasting station inserts a sync signal in front of signals transmitted in units of horizontal lines, and a receiver detects the sync signal from the transmitted signals, synchronizes the horizontal line signals, and processes the received signal. According to their types, HDTVs have different formats of transmission data of horizontal lines. FIG. 1 shows the format of data segment of US Grand Alliance (GA) HDTV, in which one data segment is made up with 832 symbols, 828 symbols for data and four symbols for a data segment sync signal. One data segment corresponds to one horizontal line of NTSC mode. The sync signal of the data segment is formed with four symbols indicative of the starting of the respective data segments, as shown in FIG. 1. Here, the data segment sync signal is made in such a certain pattern that four symbols have the signal levels of +5, -5, -5, +5, respectively. The data segment signals have random levels of signal.
For this reason, in an apparatus for receiving a transmission signal of GA mode, it must be processed after the sync signal of data segment must be detected for the first cycle of four symbols of the respective data segments for the synchronization of data segment signals received thereafter.